Often we buy products and receive a rebate coupon which can be applied towards our next purchase of the same product. If we know it is certain that we will buy the product again, it is like throwing money away to discard the rebate coupon.
This situation is analogous to the rebate of extra plant nutrients in the subsoil clay often waiting to be utilized by crops grown on Coastal Plains soils. If a test of the subsoil indicates that there is a high level of magnesium, then any recommenda tions for magnesium indicated by the plow layer soil test can be ignored. Likewise, if the subsoil tests at least high in potassium, the recommendation for potassium from the surface soil test can be reduced by as much as one-half. The subsoil test can also indicate if sulfur is needed if a separate test for sulfur is requested. Subsoil samples from fields that have been cropped for several years, however, have usually tested sufficient in sulfur.
To sample the subsoil, take samples from the top 4 inches of the clay layer at several locations in the field. Mix the clay cores in a clean container and take the sample to the nearest Clemson University Extension office for analysis by the Agricultu ral Service Laboratory. The fee is $5.00 per sample. The lab report will give the pH, CEC, percent base saturation, amounts of phosphorus, potassium, calcium, magnesium, zinc, manganese, copper and boron plus comments regarding fertilizer application re duction. The test for sulfur requires an additional $5.00 fee.
For the plants to utilize subsoil nutrients efficiently, subsoiling may be necessary to insure that a hard-pan will not deter access of the roots to the subsoil. The subsoil clay should also be no greater than 15 to 20 inches from the soil surface and have a pH value greater than about 5.0.